The present invention relates to a ferroelectric element such as an FeRAM utilizing a non-volatile property of a ferroelectric material, a semiconductor device using the ferroelectric element, and a method of manufacturing the ferroelectric element. The present invention also relates to a high dielectric element such as a DRAM utilizing a high dielectric constant and a low leakage current density, a semiconductor device using the high dielectric element, and a method of manufacturing the high dielectric element.
As a semiconductor memory, there is a DRAM (Dynamic Random Access Memory) having the ability of rewriting data at a high speed. DRAMs have been produced which have a large capacity of 16 M bits to 64 M bits in response to the progress of these technologies for realizing a higher density and a higher integration. Such large capacity also requires a technology for achieving finer geometries for circuit components, particularly, finer geometries for capacitors for storing information. For achieving finer geometries for capacitors, it is required to provide a thin dielectric film, to select a material having a high dielectric constant, and to change the structure of the capacitor composed of upper and lower electrodes and a dielectric material from two-dimensional to three-dimensional. With respect to a high dielectric material, it is known that BST (Ba/Sr)TiO3 having a simple lattice perovskite crystal structure exhibits a dielectric constant (xcex5) larger than that of SiO2/Si3N4. An example of the use of such a high dielectric material has been reported in International Electron Device Meeting Technical Digest (IEDM Tech. Dig.), p. 823, 1991.
A non-volatile memory FeRAM (Ferroelectric Random Access Memory) using a ferroelectric material as a capacitor material has a characteristic capable of storing data in the OFF state of a power supply because it utilizes two residual polarization states which are different in polarity. The FeRAM has a feature in terms of rewriting data at a speed which is very high, such as the order of xcexcs or less, and therefore, it is expected to provide an ideal memory in the next generation. In the case of such a FeRAM, it is also required to provide a thin ferroelectric film for achieving a large capacity. Incidentally, a semiconductor memory intended to suppress reactivity between a ferroelectric material and a metal electrode has been disclosed in Japanese Patent Application Laid-open No. 5-190797, in which PZT (lead zirconate titanate) is used as a ferroelectric material and a silicon nitride (SiNx) film operating as a diffusion preventive layer is formed around the ferroelectric material.
The above-described technologies, however, have failed to examine the suppression of the leakage current density accompanied by thinning of a dielectric material essentially to be performed for increasing the degree of integration. A memory using the above-described BST has the object of lowering an operational voltage along with higher integration. For lowering the operational voltage of a memory, it is required to ensure a sufficient capacitance at a small voltage. To increase such a capacitance, it has been proposed to select a material having a high dielectric constant, to increase the electrode area, and to make the high dielectric material thin. A thin film made of BST having a polycrystalline structure, however, has a problem in terms of withstand voltage characteristic because such a polycrystalline film allows leakage current to easily flow through grain boundaries of the crystals. For this reason, in the case of using the BST thin film as a capacitor, it is difficult to apply a sufficient operational voltage thereto.
In the above described ferroelectric capacitor, in which a silicon nitride film is formed around the PZT film, the silicon nitride film acts as a diffusion preventive layer capable of preventing thermal diffusion from elements of PZT, thereby maintaining a desirable stoichiometric composition of the ferroelectric material necessary for ferroelectric characteristics. The silicon nitride layer in the above-described ferroelectric capacitor, however, has a problem. Since the silicon nitride film has a dielectric constant as small as 7, it must be formed to an ultra-thin thickness of 30 xc3x85 or less for suppressing a lowering of the total capacitance of the ferroelectric capacitor having a size of 4 xcexcm2. Further, in the case of a higher integration in the order of 1 G bits, the area of the capacitor becomes as small as 0.1 xcexcm2. In this case, it becomes apparent on the basis of simple calculation that the silicon nitride layer must be formed to a further ultra-thin thickness of 1 xc3x85 or less.
Additionally, in the thinning process used in the prior technologies, if a metal is as an electrode, there occurs a problem that a transition layer is formed by diffusion of an element at an interface between a dielectric thin film and the metal electrode, to thereby reduce spontaneous polarization (Pr), to increase field reversing (Ec), and to give rise to film fatigue.
To solve the above-described problems, the present invention has been made, and an object of the present invention is to provide a high dielectric layer containing insulating particles, which is capable of suppressing leakage current flow through grain boundaries of crystals and which can be thinned to such an extent as to meet a requirement of high integration; a high dielectric element in which the high dielectric thin film is sandwiched between upper and lower electrodes; a semiconductor device using the high dielectric element; and a method of manufacturing the high dielectric element.
Another object of the present invention is to solve the above-described problems and to provide a ferroelectric layer containing insulating particles, which is capable of suppressing leakage current flow through grain boundaries of crystals and which can be thinned to such an extent as to meet a requirement of high integration; a ferroelectric element in which the ferroelectric thin film is sandwiched between upper and lower electrodes; a semiconductor device using the ferroelectric element; and a method of manufacturing the ferroelectric element.
A further object of the present invention is to provide a high dielectric element or a ferroelectric element including the above mentioned high dielectric thin film or the above mentioned ferroelectric thin film having a thickness of 200 xc3x85 or more, wherein the element can be supplied with an operation voltage of 2 V for operating a semiconductor memory.
A further object of the present invention is to provide a high dielectric element in which a conductive oxide is used as an electrode which is in contact with the above mentioned high dielectric thin film to suppress formation of a transition layer, and a method of manufacturing the high dielectric element.
A further object of the present invention is to provide a ferroelectric element in which a conductive oxide is used as an electrode which is in contact with the above mentioned ferroelectric thin film to suppress formation of a transition layer, and a method of manufacturing the ferroelectric element.
To achieve the above objects, according to the present invention, there is provided a ferroelectric element including an upper electrode, a ferroelectric thin film, and a lower electrode, wherein the ferroelectric layer contains insulating particles having a resistance of 106 xcexa9 or more.
According to the present invention, there is provided a high dielectric element including an upper electrode, a high dielectric thin film, and a lower electrode, wherein the high dielectric layer contains insulating particles having a resistance of 106 xcexa9 or more.
The insulating particles have particle sizes each being in a range of 50 xc3x85 or less.
The ferroelectric thin film may be made of a material selected from the group consisting of a material expressed by (Pb1xe2x88x92xAx)(Zr1xe2x88x92yTiy)O3 (where A is one element selected from the group consisting of La, Ba, and Nb), and a material expressed by (AO)2+(Byxe2x88x921CyO3y+1)2xe2x88x92 (where A is at least one element selected from the group consisting of Tl, Hg, Pb, Bi, and a rare earth element; B is at least one element selected from the group consisting of Bi, Pb, Ca, Sr, and Ba; and C is at least one element selected from the group consisting of Ti, Nb, Ta, W, Mo, Fe, Co, Cr and Zr; and y=2, 3, 4, and 5).
The high dielectric thin film may be made of one material selected from the group consisting of a material expressed by (Ba1xe2x88x92xSrx)TiO3 and a material expressed by (Pb1xe2x88x92xAx)(Zr1xe2x88x92yTiy)O3 (where A is one element selected from the group consisting of La, Ba and Nb).
The insulating particles may be those of a compound containing Si.
The lower electrode may be composed of a metal, a conductive oxide of a single element, and a conductive oxide having a perovskite structure, which are formed on a base substrate in this order, and each of the conductive oxides may be oriented along a specific plane.
The upper electrode may be composed of a conductive oxide having a perovskite structure and a metal or it may comprise a conductive oxide having a perovskite structure, a conductive oxide of a single element, and a metal, which are formed in this order from the side in contact with the ferroelectric thin film or the high dielectric thin film.
In the case where the ferroelectric thin film has a thickness of 200 xc3x85 or more, the ferroelectric element may exhibit a withstand voltage of 2 V or more at a leakage current density of 10xe2x88x925 A/cm2 or less.
In the case where the high dielectric thin film has a thickness of 200 xc3x85 or more, the high dielectric element may exhibit a withstand voltage of 2 V or more at a leakage current density of 10xe2x88x925 A/cm2 or less.
The metal used for the electrode may be at least one metal selected from the group consisting of Pt, Au, Al, Ni, Cr, Ti, Mo, and W. Also, to realize the function of the electrode material, a conductive oxide of a single element or a perovskite structure, which has a resistivity of 1 mxcexa9xc2x7cm or less, may be used as the electrode. The conductive oxide of a single element may be an oxide of at least one element selected from the group consisting of Ti, V, Eu, Cr, Mo, W, Rh, Os, Ir, Pt, Re, Ru and Sn. The conductive oxide having a perovskite structure may be at least one kind of perovskite oxide selected from the group consisting of ReO3, SrReO3, BaReO3, LaTiO3, SrVO3, CaCrO3, SrCrO3, SrFeO3, La1xe2x88x92xSrxCoO3 (0 less than x less than 0.5), LaNiO3, CaRuO3, SrRuO3, SrTiO3, and BaPbO3, and has a resistivity of 1 mxcexa9xc2x7cm or less.
According to the present invention, there is provided a method of forming the ferroelectric thin film, including the step of forming the ferroelectric thin film by sputtering in an atmosphere of a mixed gas of oxygen and an inert gas at a temperature of 650xc2x0 C. or less. In addition, the film formation temperature is selected to suppress reaction with an electrode. Instead of the sputtering method described above, the ferroelectric thin film may be formed by MOCVD in an atmosphere of oxygen or excited oxygen at a temperature of 650xc2x0 C. or less.
According to the present invention, there is provided a method of forming a ferroelectric thin film, including the step of forming the ferroelectric thin film by applying a starting material composed of a metal alkoxide or a metal salt of an organic acid on a substrate by spin-coating or dip-coating and baking the film at a normal pressure and at a temperature of 650xc2x0 C. or less. In addition, the film formation temperature is selected to suppress a reaction with the electrode.
According to the present invention, there is provided a method of forming a high dielectric thin film, including the step of forming the high dielectric thin film by sputtering in an atmosphere of a mixed gas of oxygen and an inert gas at a temperature of 650xc2x0 C. or less. In addition, the film formation temperature is selected to suppress reaction with the electrode. Instead of the sputtering method described above, the high dielectric thin film may be formed by MOCVD in an atmosphere of oxygen or excited oxygen at a temperature of 650xc2x0 C. or less.
According to the present invention, there is provided a method of forming a high dielectric thin film, including the step of forming the high dielectric thin film by applying a starting material composed of a metal alkoxide or a metal salt of an organic acid on a substrate by spin-coating or dip-coating and baking the film at a normal pressure and at a temperature of 650xc2x0 C. or less. In addition, the film formation temperature is selected to suppress a reaction with the electrode. According to the present invention, there is provided a method of forming the conductive oxide of a single element or a perovskite structure, including the step of forming a conductive oxide of a single element or a perovskite structure by sputtering in an atmosphere of a mixed gas of oxygen and an inert gas at a temperature of 650xc2x0 C. or less. Instead of the sputtering method described above, the conductive oxide of a single element or the perovskite structure may be formed by MOCVD in an atmosphere of oxygen or excited oxygen at a temperature of 650xc2x0 C. or less.
According to the present invention, there is provided a method of forming the conductive oxide of a single element or the provskite structure, including the step of forming the conductive oxide of a single element or the provskite structure by applying a starting material composed of a metal alkoxide or a metal salt of an organic acid on a substrate by spin-coating or dip-coating and baking the film at a normal pressure and at a temperature of 650xc2x0 C. or less. In addition, the film formation temperature is selected to suppress a reaction with an electrode.
Further, in the step of forming the ferroelectric thin film from a stating material composed of a metal alkoxide or a metal salt of an organic acid by spin-coating or dip-coating, the ferroelectric thin film may be formed while irradiating ultraviolet rays to the ferroelectric thin film. This is based on the knowledge that the decomposition of a raw material caused by light irradiation is considered effective for lowering the film formation temperature. The high dielectric thin film may be also formed while irradiating ultraviolet rays to the high dielectric thin film in the same manner as described above, and further, the conductive oxide may be formed while irradiating ultraviolet rays to the high dielectric thin film in the same manner as described above.
According to the present invention, there is provided a semiconductor device, wherein the structure including the upper electrode, the ferroelectric thin film, and the lower electrode is formed as a capacitor in a structure of a field effect transistor.
Further, according to the present invention, there is provided a semiconductor device, wherein the structure including the upper electrode, the high dielectric thin film, and the lower electrode is formed as a capacitor in a structure of a field effect transistor.